Search Results

High noise at Operator Ear Level (OEL) of tractor is the major cause of fatigue to the operator. With growing competition, and upcoming legislative requirement there is ominous need for the agricultural tractor manufacturers to control noise levels. Objective of the present study is noise reduction on agriculture tractor by identifying and controlling key noise sources unaffecting performance parameters like power, torque and fuel efficiency to meet upcoming noise legislations. Noise Source Identification (NSI) is carried out to identify and rank airborne and structure borne noise sources. The airborne sources such as cooling fan, exhaust silencer and intake are evaluated using elimination method at tractor level. The NSI on engine is carried out separately in hemi anechoic chamber to identify the major noise radiating components by using noise and vibration measurement, sound intensity mapping tools.

Exhaust noise is the major noise source for the automotive vehicle contributing to its interior as well as exterior noise. The Transmission Loss (TL), noise reduction, Insertion Loss (IL) and radiated noise are the major characteristics used to describe the performance of a muffler in an automotive exhaust system. Out of these characteristics, Insertion loss and exhaust radiated sound pressure levels plays a significant role in muffler design as it is a measure of true performance of muffler along with engine/vehicle and very much useful for the designers to compare different silencer configurations. In present work, the sound source is modelled by acoustic impedance and volume velocity of the engine. Since it is difficult to estimate the sound source impedance of the exhaust by measurements either with direct or indirect methods as both are prone to errors and difficult to implement, the empirical equations are used to define exhaust source, to have reasonable accuracy.

Acoustic Holography is emerging as a powerful, high-resolution noise source localization technique in this decade. Compared to conventional sound intensity measurement, Acoustic Holography scores because of its ability to provide on-line visualization of acoustic energy distribution of the sources perform measurements during stationary and transient conditions and it is substantially faster and easier. Further, with Near Field Acoustic Holography (NAH) and Beam-Forming (BF) techniques, it is possible to cover wide range of frequencies with reasonable investment. This paper compares and evaluates the advantages of the Acoustic Holography technique with conventional Sound Intensity Mapping for different applications such as noise mapping of a vehicle, noise source identification of engine and other small sized components. It also discusses how this technique can be extended to moving sources such as noise source identification during pass-by.